The present invention relates to an actuator which uses a shape memory alloy and which is capable of performing a continuous rotational motion in the forward and reverse directions.
Conventionally, as a continuous rotary actuator, an electromagnetic motor and a motor for using an effect of recovering to the original shape, namely, a shape memory effect of a shape memory alloy (SMA), as rotation torque are well known.
The above-mentioned electromagnetic motor has problems in that the weight is too large to minimize because a coil is used, and if minimized, the coil becomes small and thus has a decreased output (torque).
On the other hand, the motor using the shape memory alloy has problems in that the motor needs a complicated switching circuit for the driving system, so that it is difficult to realize a small and lightweight motor and the rotation cannot be locked when it is not energized.
The present invention has been made in consideration of the above-described problems and an object of the invention is to provide a continuous rotary actuator using a shape memory alloy, which has a simple structure, being small and lightweight, which has a high torque, and in which the rotation can be locked in a non-energized state.
It is another object of the present invention to provide a continuous rotary actuator using a shape memory alloy, in which continuous rotation in the forward and reverse directions is possible.
The above and other objects and new features of the present invention will be apparent by the description of the specification and the appended drawings.
In order to achieve the above objects, the continuous rotary actuator using the shape memory alloy according to the present invention is characterized by comprising: an inner drum in an outer cylinder, the inner drum rotating around the axis as a rotating shaft, wherein both ends of a first and second shape-memory-alloy torsion springs are attached to a pair of movable contact members disposed between the outer cylinder and the inner drum, wherein one of the torsion springs are unwound to recoil by electrical heating of one of the torsion springs and another torsion spring is wound accordingly in the opposite direction, and wherein the movable contact members can be freely engaged with the outer cylinder and the inner drum via engaging means in which when one of the movable contact members is engaged with the outer cylinder, another is engaged with the inner drum; and switching means for alternately switching the electrical heating of the first and second shape-memory-alloy torsion springs according to the rotation of the inner drum, thereby continuously rotating the inner drum in one direction. A plurality of pairs of the first and second shape-memory-alloy torsion springs can be used.
In the continuous rotary actuator, the outer cylinder and the inner drum are connected to power supplies each having different polarity, and the switching means may be a one such that the movable contact members engaged with the outer cylinder and the inner drum can selectively energize the first and second shape-memory-alloy torsion springs according to its engaging state. In addition, the switching means has a movable cylinder constructing the movable contact member, wherein the movable cylinder encloses a pair of shape-memory-alloy coil springs in a manner so as to transform one coil according to the recoil of the other due to the electrical heating, and also which has contacts for applying current to the coil springs necessary for rotating the inner drum by coming into contact with conductive bars at the engaging positions of the outer cylinder and the inner drum.
Furthermore, the continuous rotary actuator has concave portions with which the movable cylinders are removably engaged in a manner so as to face each other at equally spaced positions of the inner periphery of the outer cylinder and the outer periphery of the inner drum. In addition, diodes each having a different directional characteristic are connected to the energizing system of the first and second SMA torsion springs, thereby enabling either one of the SMA torsion springs to be energized depending on the polarity of the power supply connected via the movable contact member.
The inner drum is formed by joining different directional ratchet gears and may be provided with two-way ratchets engaging with the concave portions between the teeth of the ratchet gears.
In the continuous rotary actuator according to the present invention, the first or second SMA torsion spring is electrically heated in a state in which one of the movable contact members is engaged with the outer cylinder and another is engaged with the inner drum, and when the engaging state of the movable contact members is changed, at the same time the appropriate SMA torsion spring is electrically heated, and as a result, the inner drum can be continuously rotated.